1. Field of the Invention
The present invention relates to a process for the production of chlorinated ethylene-propylene copolymers by chlorinating ethylene-propylene copolymers in an aqueous suspension. More specifically, it relates to a process for the production of chlorinated ethylene-propylene copolymers which are not only excellent in heat resistance and cold resistance, but are also excellent in oil resistance and, further, are excellent in weather resistance and ozone resistance and can not only be cross-linked, but are also relatively easily vulcanized.
The present invention also relates to chlorinated ethylene-propylene copolymer compositions with excellent vulcanization ability and cross-linking ability. More specifically, it relates to chlorinated ethylene-propylene copolymer compositions comprised of (A) chlorinated ethylene-propylene copolymers, (B) thiourea compounds, (C) sulfur and/or sulfur donors, (D) metal compounds acting as acid accepting agents, and, in some cases, (E) dithiocarbamates or mercaptotriazinic compounds, which compositions are not only excellent in vulcanization ability, but also are excellent in flexibility and compression set and further are excellent in heat resistance.
The present invention further relates to chlorinated ethylene-propylene copolymer compositions with excellent cross-linking ability comprised of (A) chlorinate ethylene-propylene copolymers and (G) organic peroxides, which compositions are not only excellent in cross-linking ability, but also excellent in flexibility and compression set and further are excellent in heat resistance.
2. Description of the Related Art
Chlorinated ethylene-propylene copolymers are generally excellent in oil resistance, flame retardance, etc. so are useful as paints and adhesives, as has been known in the past (see Japanese Unexamined Patent Publication (Kokai) No. 59-122503). As the process for chlorinating ethylene-propylene copolymers, there is the process wherein ethylene-propylene copolymers are chlorinated in an aqueous medium not containing a suspending agent at a first stage at less than 50.degree. C., for example, 20.degree. to 45.degree. C., until 2% by weight or more, for example, 2 to 15% by weight, then the temperature raised to 50.degree. C. or more, for example, 70.degree. to 100.degree. C., at a second stage, and chlorination performed at that temperature until a chlorine content of 18% by weight or more, for example, 18 to 50% by weight. Further, there has been proposed the process wherein ethylene-propylene copolymers are dissolved in a solvent such as, for example, carbon tetrachloride, and the chlorination performed in the solvent at a relatively high temperature, up to 150.degree. C. However, this process involves a high vapor pressure of the solvent in the reaction system and requires high temperature pressure resistant reaction vessels. Further, there are problems in the heat stability of the synthesized polymer. On the other hand, when chlorinating with the above-mentioned aqueous medium, there are problems in that the chlorinated substance agglomerates in the rinsing after the chlorination.
Chlorinated polyethylene, in particular noncrystalline chlorinated polyethylene rubber substances, is chemically saturated in structure and is a chlorine-containing polymer substance, so its cross-linked products (or vulcanized products) are excellent in physical properties such as weather resistance, flame retardance, chemical resistance, electrical properties, and heat resistance. Therefore, it is used in a wide range of industrial fields formed into cable coverings, electrical components, hoses, building materials, auto parts, packing, and sheets.
However, this chlorinated polyethylene differs from general use rubber, for example, rubber principally composed of butadiene, in that it is, as mentioned above, chemically saturated in structure, so is difficult to vulcanize using sulfur or sulfur donors as the vulcanization agent. Therefore, as the cross-linking agent, use is generally made of organic peroxides for the cross-linking. However, when hoses, sheets, tubes, or other products are extruded and then cross-linked using the vulcanization vessels generally used in the rubber industry, it is difficult to obtain the suitably cross-linked product and the resultant cross-linked product is inferior in, for example, tensile strength, heat resistance.
For the above reasons, it has been proposed to vulcanize the substance using sulfur or a sulfur donor (see Japanese Unexamined Patent Publication (Kokai) No. 55-71742). Further, some of the present inventors have previously proposed the formulation into the sulfur or sulfur donor of thiourea compounds, metal salts or dithiocarbamate, and, as an acid accepting agent, magnesium oxide and/or lead oxide so as to obtain a vulcanizable chlorinated polyethylene composition able to be vulcanized and excellent in various mechanical properties such as tensile strength (see Japanese Unexamined Patent Publication (Kokai) No. 61-209244).
However, the composition, as clear from a comparison of the cross-linking curve of FIG. 1, is not always satisfactory in vulcanization ability and, therefore, not sufficient in flexibility and compression set and, further, is inferior in heat resistance.
On the other hand, the process of cross-linking using organic peroxides enables formation of compositions with excellent heat resistance and compression set, but the compositions are poor in cross-linking efficiency so require use of large amounts of organic peroxides or further cross-linking agents in the case of products for which high heat resistance and high compression set are required, leading to increased costs.